US3991401A - Method of recognizing words for an associative store and an optical device for implementing said method - Google Patents

Method of recognizing words for an associative store and an optical device for implementing said method Download PDF

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US3991401A
US3991401A US05/567,405 US56740575A US3991401A US 3991401 A US3991401 A US 3991401A US 56740575 A US56740575 A US 56740575A US 3991401 A US3991401 A US 3991401A
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bits
row
words
logic
modulating
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Luigi d'Auria
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
    • G11C13/042—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam using information stored in the form of interference pattern
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C15/00—Digital stores in which information comprising one or more characteristic parts is written into the store and in which information is read-out by searching for one or more of these characteristic parts, i.e. associative or content-addressed stores

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  • the present invention relates to associative optical stores.
  • an associative store makes it possible to recognise, amongst a large number of stored words which are generally present in binary form, those which, in part or in whole, are identical to a given word known as the "key word," and also to pinpoint the location of these words in the store.
  • a store of this kind can make it possible, for example, in a stored card index to identify those cards which contain one or more special characteristics (for example persons living in the same area in a card index of addresses, or the frequency of a word in a text); it can also be used to identify the addresses of words stored in a storage plane.
  • the searching operation carried out to determine the position of the recorded words is carried our by an operation of sequential interrogation; the interrogation time is therefore necessarily lengthy, the more so indeed the larger the capacity of the store.
  • Optical stores and in particular holographic stores combine a high storage capacity with the possibility of parallel read-out, in other words simultaneous and therefore fast read-out, of the recorded words.
  • the coherent beams A and B make it possible to record the holograms forming a store page, line by line; a line of order j simultaneously incorporates the information relating to a word a j and that relating to a word b j , in the form of as many separate holograms, all comprising the bits of b j , as there are bits in a j ; each hologram occupies in the line or row, one or the other of two distinct positions depending upon whether the bit a j with which it is associated has the value 0 or 1, the bits of a i thus being coded by position of their associated hologram.
  • a coherent beam A l projects on to the hologram page thus obtained, a set of spots, each spot coinciding in each line or row, with one or the other of the two possible positions of each recorded hologram; all lines of the spots are identical, each containing one and the same key word A l , coded in the form of its binary complement by the position of the spots in the line. Any hologram coinciding with a spot, will reconstitute the word b j which has been used to record it.
  • the method of word recognition in an associative store and the device implementing said method, which forms the object of the present invention, makes it possible to overcome the two above mentioned drawbacks of the prior art.
  • the store planes utilised by the method and device described hereinafter contain the binary information in an optically recorded form, the recording having been effected either directly or by a holographic procedure, and when lighted by a luminous read-out beam, restore the recording in the form of light spots projected simultaneously on the two identical regular arrays of photodectors which perform the read-out function. Due to this double read-out, each bit in the store plane can be recorded without its complement, the value 1 corresponding to the presence of a light spot, and the value 0 to the absence of a light spot.
  • the invention makes it possible to use a conventional holographic plane, produced in accordance with a prior art technique by regular array of successively recorded holograms, each corresponding to a complete page of words.
  • FIG. 1 is an explanatory diagram pertaining to the operation of holographic store plane of prior art type
  • FIG. 2 illustrates a first embodiment of the device in accordance with the invention
  • FIG. 3 illustrates the organisation of the logic processing of the signals, in accordance with the invention
  • FIG. 4 illustrates a second embodiment of the device in accordance with the invention.
  • FIG. 1 is an explanatory figure illustrating the operation of a holographic store plane of prior art design.
  • the store plane 1 will for example be a photographic plate upon which there have been recorded a certain number of holograms such as 1p, this in form of the variations in the transparency of the emulsion; these holograms are regularly arranged upon the plate in the form of a regular array, and each of them is the hologram of a page of the store.
  • a coherent light beam 10 makes it possible to illuminate one or the other of these holograms.
  • Each hologram when illuminated by the beam 10, transforms the latter into a set 11 of convergent beams such as 11i; whatever the hologram, all the beams converge in a same plane 12 where they project the image of the page recorded by the corresponding hologram, in the form of a set of light spots such as 12i, the latter being the point of convergence of the beam 11i.
  • These light spots on the plane 12, occupy a certain number of nodes of an array of M rows and N columns, and, in binary notation, indicate the presence of a 1 bit; the nodes of the array at which there is no light spot correspond to 0 bits.
  • the page whose image is projected on to the plane 12 is selected.
  • the images of the different pages are projected in accordance with the nodes of a same array, so that they can be read out by an array of photodetectors arranged at a fixed position in the plane 12.
  • the store plane 1 comprises an array of four holograms corresponding to four store pages.
  • the image of each page forms an array of three rows and three columns; each row represents a coded binary word, the store page thus comprising three words of three bits each, respectively working from top to bottom (101), (010) and (100).
  • the information density of the holographic store planes may be much higher, for example, in each plane, around a thousand holograms comprising 30 words of 30 bits each.
  • the invention proposes a method of recognizing words, which is applicable to an associative store and which makes it possible to utilize without modification, any conventional optical store plane similar to that described in FIG. 1. To illustrate this procedure, it will be applied to the store plane illustrated by said same figure.
  • the first set may contain one or the other of the words 100, 101, 110 and 111, the second 100 and 000; in the selected page, the words 100 and 101 will be classified in the first set and the word 100 in the second (it will be seen that words such as 010 may not be classified in either of the two sets).
  • the words, if they exist, which belong simultaneously to the two sets (in the present case, the word 100) are thus identified as being identical to the key word.
  • the classification of the words in each page as belonging or not belonging, respectively to the first and second sets, is carried out simultaneously on first and second identical images of the same page.
  • each bit of each image there can be associated a logic signal which acquires a value s l in respect of bits of value 1, and s o , which is less than s l , in respect of bits of value 0.
  • the regular array arrangement of the words in the page is exploited in order to arrange that the only bits truly associated with signals, are those located in the same columns as the bits of value 1 of the key word, in the case of the first image, and as the bits of value 0 in the case of the second image.
  • All the signals coming from the bits of a same word, and therefore from a same row, are added in order to furnish a row signal S i l for the first image, and a row signal S j O for the second image, characteristic of each word in each image.
  • Each of these signals is compared with a single threshold value for each image, S S l in the case of the first, S S O in the case of the second; these two threshold values are linear functions of the numbers of bits having the values 1 and 0, which the key word contains.
  • the words 101 of the first row and 010 of the second row furnish row signals S 1 0 and S 2 0 , both of which have the value s 1
  • the word 100 of the third row furnishes a signal S 3 0 of value zero.
  • the threshold value S S 0 which is characteristic of the second set, will have a constant value of s 1 , whatever the number of bits and the composition of the key word; it will be shown at a later point that this threshold value S S 0 is no longer constant when the signal s 0 is other than zero.
  • the method has made it possible to classify the three words 101, 010 and 100 of the page into two sets the first of which comprises 101 and 100, and the second 100, and that the only word common to the two sets is the word appearing in the second row, namely 100, which indeed is identical with the key word.
  • the method as above described is applicable equally in a situation where the key word has a number P of bits, less than the number N of bits contained in each of the M words of the array; then, the task is to recognise words which contain the key word, for example, among the three words 101, 010 and 100 of the preceding example, those which contain the word 10. It is in this case, merely necessary to arrange that, simultaneously in both images, there is no signal produced from the (N - P) columns corresponding to the (n - P) non indicated bits of the key word, in fact the third column in the selected example; the words 101 and 100 thus form part of the first and of the second set, and, as such, are identified as those two words in the page which contain the key word 10.
  • FIG. 2 illustrates a first embodiment of the device in accordance with the invention, implementing the aforedescribed recognition method.
  • optical projection means comprising, like the device shown in FIG. 1, a store plane 1 where a regular array of holograms such as that lp, is recorded, a mobile laser beam 10 illuminating one or the other of said holograms in order to form the assembly 11 of convergent beams projecting onto a same plane, as shown in FIG. 1, in the form of a set of light spots corresponding bits of value 1, the image of the page recorded in the hologram.
  • a store plane 1 where a regular array of holograms such as that lp, is recorded
  • a mobile laser beam 10 illuminating one or the other of said holograms in order to form the assembly 11 of convergent beams projecting onto a same plane, as shown in FIG. 1, in the form of a set of light spots corresponding bits of value 1, the image of the page recorded in the hologram.
  • these optical projection means comprise, furthermore, a semi-transparent separator plate 100 arranged in the path of the assembly of beams 11 and dividing them into two sub-assemblies of beams, one, 110, being reflected and the other, 111, being transmitted by the plate; in this fashion, two identical images of the recorded page are obtained, respectively located in the planes 120 and 121 which are symmetrical in relation to the plane of the separator plate 100.
  • detection means 20 and 21 are arranged; they are formed by two flat sets of M linear photodetectors such as those 20i and 21i.
  • Each linear photodetector constituted by a continuous strip of photo-conductive material, is designed to receive a row of bits of the image of the projected page, and therefore a word contained by the page; it injects into a resistor such as that R0i or R1i, and thus produces a row of voltage V i 0 or V i 1 . All the resistors R0i and R1i have an identical resistance R.
  • modulating means 30 and 31 are arranged; each of them is formed by a flat assembly of N modulating bars, such as those 30j and 31j, each bar having an input which enables it to be supplied with a control volage E j .
  • FIG. 2 shows these bars as being clearly separated from the detection means, this in order to facilitate understanding of the drawing, the modulating planes are in fact virtually contiguous with the detection planes 20 and 21; the bars which form as many columns, are arranged perpendicularly to the linear photodetectors 20i or 21i and are therefore disposed parallel to the columns of the array constituting the image page.
  • the N columns of modulating means thus delimit N distinct zones; on each linear detector of the associated detection plane, each zone being associated with a bit in the word projected on to the row.
  • modulating bars are designed upon the lines of conventional electro-optical modulators, utilising for example the longitudinal electro-optical effect or Pockels effect; they are constituted, therefore, by a thin plate of a material such as deuterium monopotassium phosphate (KDP) or calcite, covered, on both the faces perpendicular to the direction of propagation of the light, by two transparent electrodes, and are arranged between crossed polarizer and analyser. In the absence of any applied field, the crystal is unixial, the optical axis being directed in accordance with the direction of propagation of the light, and the resultant modulator system is opaque.
  • KDP deuterium monopotassium phosphate
  • calcite calcite
  • the crystal In the presence of an applied field, the crystal becomes biaxial; if the polarizers are orientated at 45° to the two preferred directions of propagation of the crystal, it is then merely necessary to apply to the electrodes a voltage such that the plate produces a phase difference equal to half the illuminating wavelength; the light is rotated through 90° on passing across the plate and is then transmitted by the output polarizer; the modulator is then transparent.
  • Each colunn of the modulating means, controlled by a logic signal is thus transparent if a logical signal of value 1 is applied to it, and opaque if a logic signal of value 2 is applied to it.
  • the device shown in FIG. 2 likewise comprises a control generator 4 which has N inputs for receiving the P bits composing the key words, and 2N outputs for simultaneously furnishing the control voltages E j 0 and E j 1 for the 2N modulator bars; the device of FIG. 2 also comprises logic processing means 5 designed to process the row voltages, these means incorporating 2M inputs to which to apply the row voltages V i 0 and V i 1 , and making it possible to recognise the location of the words which are being sought.
  • the means used to process the row voltages are essentially constituted by the threshold generators G0 and G1, two groups of M comparators each, C0 i and C1 i , and a group of M AND-gates Pi with two inputs and one output.
  • Each threshold generator G0 or G1 comprises N inputs designed to be supplied, from the control generator 4, with the N control voltages which are also applied to the N respective inputs of the modulating means 30 and 31, and also comprises two supplementary inputs respectively to receive a multiplier signal U o or U 1 and a voltage Vo or V1 T1, a multiplier M0 or M1 and a polarity inverter I0 or I1 and furnishes at a single output, a threshhold voltage which is a linear function of the sum of the control voltages applied to the input: S S 0 in the case of the generator G0 and S S 1 in the case of the generator G1.
  • Each comparator C0 i and C1 i is associated with a linear detector 20i or 21i in the corresponding detection plane. At one of its inputs, it is supplied with the row voltage g V i o or gV 1 1 coming from the particular row throught the medium of an amplifier A0i or A1i, all the amplifiers having the same gain g; at the other input, it is supplied with the threshold voltage gV S 0 for the comparators of the group C0, and with that gV S 1 for those of the group C1. It furnishes an output logic signal which is a function of the comparison effected between these two voltages.
  • Each gate Pi has two inputs designed to receive the logic signals, respectively from the comparators C0 i and C1 i , these signals therefore being associated with rows of the same order in the two detection planes 20 and 21. It produces a logic signal which characterizes the word recorded in the relevant row of the store page; this signal has the logic value 1, if the two input logic signals also have the value 1, and the value 0 if the contrary is the case.
  • FIGS. 2 and 3 operates in the following manner:
  • the two detection planes 120 and 121 are supplied with two identical images.
  • the plane 120 is designed to identify words which exhibit at least the same 0 values as the key word
  • the plane 121 is designed to identify words exhibiting at least the same 1 values.
  • the control generator 4 is supplied with the key word. As a function of the composition of the latter, it simultaneously generates two groups of N logic control signals each, designed in the one case to identify the 1 values, and in the other the 0 values.
  • Each column of modulating means 31 is associated, through the control generator, with a bit in the key word, the first column being associated with the first bit, the second with the second, etc.., etc.
  • the first group of N control signalsE j 1 simultaneously applied to the N modulating columns 32 j reproduces the P bits of the key word: with the 1 values of the key word there are associated control signals of logic values 1 which produce transparency in the corresponding modulating columns, and with the 0 values in the key word there are associated logic values 0 which leave the modulating columns opaque; the modulating columns are also opaque in respect of the (N - P) non indicated bits of the key words.
  • each linear detector 21i in the detection plane 21 receives light signals only in respect of the 1 values of the corresponding word, which are located in the same columns as the 1 values of the key word, since the light signals corresponding to the 1 values of the word, which are located in the same columns as the 0 values, or in other words the non-indicated bits of the key words, are intercepted by the modulating means.
  • R is the common resistance of the resistors R0i and R1i. This row voltage characterizes all the words belonging to the first set or the set of words exhibiting at least the same as 1 values as the key word.
  • the row voltage whose value is closest, corresponds to words in respect of which a 0 is substituted for a 1 in a single transparent column; this voltage can therefore be taken as the threshold voltage V S 1 :
  • the threshold generator G1 is supplied with the first group of N control signals E 1 1 , which are also supplied to the modulating means 31. From a signal gP 1 proportional to the number P 1 of logic signals having the value 1 which are contained in the group of N signals, it furnishes a reference voltage gV S 1 to the M comparators C1i which receive said voltage at their "minus" inputs.
  • the comparators C1i are also supplied, at their "plus” inputs, via the amplifiers A1 i , with the row voltage gV i 1 coming from the corresponding linear photodetector 21i. They emit a logic 1 signal in respect of all the V i 1 signals which exceed the threshold V S 1 , thus in respect of all the words belonging to the first set; words not belonging to the first set, are characterized by the logic signal 0.
  • Identification of the words of the second set namely those which exhibit at least the same 0 values as the key word, is carried out in very much the same fashion by the detection means 20 and the modulating means 30, which are associated with the comparators C0i and with the threshold generator G0.
  • the control generator produces a second group of N logic control signals E j 0 which are this time complementary to the bits of the key word in respect of the P indicated bits, and have the value 0 in respect of the non-indicated bits.
  • the modulating columns 30j are then transparent when they are associated with the 0 bits of the key word, and opaque when associated with the 1 bits or non-indicated bits. No zone of any of the linear detectors 20i can receive any light signal unless it is located in a column corresponding to a 0 bit of the key word; it does not in effect receive any light signal and only produces a current i 1 if the bit read-out has the value 1.
  • This voltage gV S 0 is applied to the "plus” inputs of the M comparators C0i which compare it with the row voltage gV i o coming from the associated linear photodetector 20i applied to the "minus” input; the comparators whose "minus” inputs are supplied with a voltage gV i 0 which is lower than the threshold voltage gV S 0 produce a logic 1 at their output, thus characterising words which belong to the second set.
  • P l and P o the respective numbers of the bits of value 1 and 0, contained in the key word.
  • the value which must be given to the threshold voltage is that of the row voltage which is nearest below that obtained by projecting on to one of the linear detectors belonging to the first detection means, the key word possibly supplemented by 0 values.
  • the threshold voltage will therefore be equal to the row voltage produced by a word comprising, in the P 1 same columns as the 1 values of the key word (columns with transparent bars), (P 1 - 1) bits of values 1 and one bit of value 0, and comprising (N-P 1 ) bits of value 1 in the other columns (which have opaque bars), namely:
  • the threshold voltage V S 1 can be placed in the form of a linear function of P 1 :
  • the value which must be given to the threshold voltage is that which is immediately above the row voltage value obtained by projecting upon the second detection means, the key word possibly supplemented by 0 values. It will therefore be equal to the row voltage produced by a word comprising, in the P 0 same columns as the 0 values of the key word (columns associated with transparent bars), (P 0 -1) bits of value 0 and one bit of value 1, and, in the (N-P O ) other columns, (associated with opaque bars), (N-P 0 ) bits of value 0, in other words:
  • the threshhold generator GO is supplied at the N inputs of the adder SO, with the second group of control signals, made up of P 0 logic 1 signals corresponding to the P 0 bits of the value 0 in the key word), and (N-P 0 ) 0 logic signals (corresponding to the (P-P 0 ) bits of value 1 and the (N-M+P 0 ) non indicated bits, of the key word), picked off from the N outputs of the control generator, which go to second modulating means; the adder SO furnishes a voltage proportional to P 0 , namely - g P 0 , to the input of the multiplier MO which latter is also supplied at the first of the two supplementary inputs of the generator, with the signal: u 0 ; the multiplier thus produces the voltages g P 0 u 0 .
  • This latter voltage is applied to one of the inputs of the second adder TO which is also supplied, from the second supplementary input of the generator, with the voltage gV 0 and itself produces the voltage: g (P 0 u 0 + V 0 ).
  • the threshold generator G 1 is supplied at N inputs with the first group of N control signals coming from the N first outputs of the control generator; this group comprises P 1 1 signals, associated with the P 1 bits of value 1 in the key word, and with (N-P 1 ) 0 signals associated with the bits of value 0 or non-indicated bits, in the key word.
  • the threshold generator G1 is furthermore supplied with the voltage u 1 ; at the second supplementary input it receives the voltage gV 1 .
  • the threshold generator G 1 furnishes the threshold voltage:
  • the invention also proposes a second embodiment of the device, designed to implement the process described initially, which embodiment makes it possible to overcome the limitation imposed by the transparency of the modulating bars.
  • the overall disposition of the store plane 10, the separating plate 12 and the detection means 20 and 21, as shown in FIG. 2, is retained, as also are the links between the control generator 4 and the modulating means 30 and 31, on the one hand, and those between the detection means 20 and 21 and the logic processing means 5, on the other.
  • the modulating means 30 and 31, which have been shown in planes distinct from those containing the detection means 20 and 21, are then located either in the same planes 120 and 121 as said latter, or behind said planes.
  • FIG. 4 describes the relative arrangement of the detection means 20 (or 21) and the modulating means 30 (or 31), within the context of the second embodiment of the device.
  • the detection and modulating means have been illustrated as being disposed in one and the same plane 120 (or 121), which is the plane on to which there is projected one of the two images of the store page; the same connecting diagram can be produced by arranging the modulating means behind (considered in relation to the direction of propagation of the light rays) the plane which contains the detection means.
  • the detection means 20 are constituted by a regular array of M rows each containing N separate photodetectors D ij , each photodetector receiving one bit of the image.
  • the modulating means 30 are constituted by a regular array of N columns each comprising M analogue gates C ij .
  • Each photodetector D ij of the array 20 (or 21) is connected in series with an analogue gate C ij of the array 30 (or 31), between a bias voltage V p which is common to all the photodetectors, and a collector line common to all the photodetectors of one and the same row of order i, each collector line itself being earthed across a resistor R.
  • Each gate C ij has a control input designed to be supplied with a control voltage E j common to all the gates of one and the same column of order j; the N control voltages E J O relating to the modulating means 30, like the N control voltages E j 1 relating to the modulating means 31, are supplied by the control generator 4 in the same form as in the first embodiment.
  • the analogue gates C ij operate as contact breakers and modulate the current produced by the associated detectors as a function of the control voltage E j applied to them.
  • the control voltage E j applied to all the gates C ij of the column of order j has the logic value 1
  • these gates behave as resistors of low resistance in series between the associated photodetector and their collecting line; each photodetectors of the column then produces a current which has the value 1 when it receives the light signal corresponding to the bit of value 1 and the value o in the absence of any light signal, that is to say in respect of bits of value 0.
  • the gate When the control voltage E j has the logic value 0, the gate has a sufficiently high resistance for the currents i 1 furnished by the photodetectors which receive a bit of value 1, and those i 0 furnished by the photodetectors which receive a bit of value 0, to be considered as zero.
  • the current furnished by the collecting line is the sum of the individual currents produced by the photodectors; at the input of the resistor R, it generates the row voltage V i 0 (ou V i 1 ).
  • the modulating columns formed by variable transparency bars acting upstream of the photodetectors in order to modulate the luminous intensity received by these latter, have been replaced by modulating columns formed by variable-resistance gates acting downstream of the photodetectors in order to modulate the current produced;
  • the device in accordance with the invention in both its first and its second embodiment, has been described in relation to the case where the projected store page is stored in the form of a hologram belonging to a holographic store plane.
  • the foregoing clearly shows that the operation of this device in no way depends upon the form in which the store is filled provided that the projected page appears in the form of uniformly disposed light spots.

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Citations (4)

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US3614191A (en) * 1968-03-29 1971-10-19 Nippon Electric Co Associative memory employing holography
US3720453A (en) * 1971-06-01 1973-03-13 Honeywell Inc Differential readout holographic memory
US3781830A (en) * 1972-06-23 1973-12-25 Rca Corp Holographic memory with light intensity compensation means
US3887906A (en) * 1972-06-28 1975-06-03 Honeywell Inf Systems Optical associative memory using complementary magnetic bubble shift registers

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3614191A (en) * 1968-03-29 1971-10-19 Nippon Electric Co Associative memory employing holography
US3720453A (en) * 1971-06-01 1973-03-13 Honeywell Inc Differential readout holographic memory
US3781830A (en) * 1972-06-23 1973-12-25 Rca Corp Holographic memory with light intensity compensation means
US3887906A (en) * 1972-06-28 1975-06-03 Honeywell Inf Systems Optical associative memory using complementary magnetic bubble shift registers

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Title
Cobb et al., "Associatively Addressed Holographic Storage," IBM Tech. Disclosure Bulletin, vol. 13, No. 5, 10/70, pp. 1070-1071. *
Gabor, "Associative Holographic Memories," IBM J. Res. Develop., Mar. 1969, pp. 156-159. *
Sakaguchi et al., "A New Associative Memory System Utilizing Holography," IEEE Transactions On Computers, vol. C-19, No. 12, 12/70, pp. 1174-1181. *

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FR2268329B1 (cs) 1978-12-29

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